1. Field of the Invention
The present invention relates to a verification of an electronic weighing machine, particularly to a verification system for a large-scale fixed electronic weighing machine which belongs to a measurement verification technique.
2. Description of the Related Art
A fixed electronic weighing machine is the maturest weighing implement in the world, which is popularly applied to weigh the various vehicles and wares in metallurgical industry, chemical industry, railway, harbor, and industrial and mining enterprises, and also applied to control the weighing procedure of the trading settlement and the producing process. The weighing machine is an ideal weighing implement for the enterprises to enhance the level of modern weighing. The principle of the fixed electronic weighing machine is to set weighed objects or loading vehicles on a weighing platform. Under the effect of weight, the weighing platform transmits the weight to a swinging supporting such as the steel balls and press head, and the flexible unit of the weighing sensor is deformed, which renders a foil gauge bridge-circuit adhered to the flexible unit, lose the balance and output an electric signal in a positive proportion with the weight value. The signal is magnified by a linear magnifier, converted into a digital signal via A/D, and then processed by a microprocessor of a gauge to directly display the weight value.
The fixed electronic weighing machine must be verified to confirm its accurate level before use. The large-scale weighing machine needs to be verified again to ensure its accurate level when using for a time or changing the components thereof so as to correspondingly adjust for satisfying the demand of accuracy. A conventional standard instrument used for fixed electronic weighing machine for verifying is divided into three types. The fixed electronic weighing machine of the standard number stipulated by GB7723-2008 is adopted by the international proposal OIML R76 “The non-automatic weighing machine” (2006E) clearly points out three permitted standard instruments for verifying as follows: 1. a counterweight, concretely to a standard counterweight or a standard quality; 2. an auxiliary verification device, concretely to an auxiliary verification device equipped in the weighing machine or an independent auxiliary verification device; 3. a substitution of the standard counterweight used in verification, concretely to part of the standard counterweights and other substitutions that are able to be irregularly fixed and loaded.
However, the standard instrument for verifying the weighing machine is regulated in the regulation of verification of the digit indicator weighing machine stipulated by JJG539-1997: 1. the standard counterweight; 2. the standard counterweights and the substitutions of the standard counterweights. Therefore, the standard instrument presently used for verifying the fixed electronic weighing machine is the standard counterweights or standard counterweights and its substitutions, and the auxiliary verification weighing machine is not adopted to be a standard instrument for verifying the fixed weighing machine. In the international proposal of R76 “The non-automatic weighing machine” and the fixed electronic weighing machine stipulated by the national standard GB7723-2008, the auxiliary verification device is only regulated as follows: A maximal permissible error of an auxiliary verification device equipped in the weighing machine or an independent auxiliary verification device should be ⅓ of the maximal permissible error of the verification load. What the auxiliary verification device is which is not mentioned in the international proposal and the GB7723-2008, only a maximal permissible error of the auxiliary verification device is regulated. So far, the documents of adopting the independent auxiliary verification device to perform in verifying a large-tonnage fixed weighing machine on the spot have rarely been seen.
Referring to the China patent number CN86105843 published in 17 Feb. 1988, by “A verification device of truck scale and track scale” is disclosed. The prior patent discloses a non-counterweight verification device. However, an accuracy of a piezometer adopted by the verification device cannot satisfy the verification accuracy demand of this type of weighing machine. Referring to the China patent number CN02230837.7 announced in 22 Jan. 2003, by “A large-scale weighing machine verification appearance” is disclosed. The prior patent also discloses a non-counterweight verification device. The prior patent comprises a verification sensor (4), a displaying gauge (7), a pressurizing device, and a pressurizing stand (3). The pressurizing stand integrates with the base used for verifying the weighing scale. The pressurizing device is fixed on the pressurizing stand. The metric accuracies of the verification sensor and the displaying gauge are larger than the metric accuracy of the verified weighing machine. The verification sensor is disposed on the body (9) of weighing machine that needs to be verified. A sphere connects the verification sensor and the pressurizing device. An output end of the verification sensor is connected to the displaying gauge. A pressure of the pressurizing device is applied on the sensor and displayed by the displaying gauge, concurrently, the pressure is also applied on the body of weighing machine needed to be verified and displayed by the displaying gauge, so the metric error of the verified weighing machine is able to be confirmed by comparing the displaying values. The verification device only verifies the in-service sensor in the weighing machine one by one. The verification device is a superposition force standard machine in practice. Nevertheless, the pressurizing and the pressurizing stand in the device are loaded manually, which cannot satisfy the demand of loading fluctuation (force value stability) and the maintaining time of the force value stability in the “JJG734-2001, the verification regulations of force standard machine” and “JJG144-2007, the verification regulations of standard force measuring gauge”. The verification process is used to verify the loading value of every in-use sensor of the weighing machine, not the span of the weighing machine. The measure accuracy of the weighing machine is not only in relation to the accuracy of every sensor, but also the hardness of the weighing platform, the foundation of the weighing platform, the accuracy of the gauge, and the adapter junction box. Although the in-service sensor of the weighing machine is qualified, the metric property of the weighing machine may not be qualified. Therefore, it is not only fully verifying the metric property of the weighing machine. The factor that affects the accuracy of the weighing machine such as the deflection of the weighing platform surface, the foundation of the weighing platform, the accuracy of the gauge, and the adapter junction box should be considered in the verification process. The prior patent can only be verified at the sensor, so the verification process cannot explain by analogy with the effective weighing status and can only similarly contrast with the in-service sensors of the weighing machine. The most important is that the weighing machine cannot be verified directly.
The current method of verifying the fixed electronic weighing machine is described as follows: Take a verification of a fixed electronic truck scale weighed 100 tons as an example and apply the standard counterweight and the substitution of the counterweight to verify according to the national standard of the fixed electronic weighing machine stipulated by GB7723-2008 or the verification regulations of the digit indicator weighing machine stipulated in JJG539-1997. Wherein, referring to FIG. 1, a fixed electronic truck scale 2′ is in a specification weighed 100 tons with three sections in length of 18 gauges, e=50 kg, m=2000. The truck scale comprises a weighing platform displaying gauge 21′, three weighing platform surfaces 211′, 212′, 213′, eight sensors 231′-238′, eight supporting points 241′-248′ disposed on top of the sensors, and eccentric test areas 251′-258′ correspondingly disposed around the respective support points as shown by the dotted line in FIG. 1. While verifying, put the standard counterweight or the substitution 3′ of the standard counterweight on each unbalanced loading test area to proceed an eccentricity test sequentially. The specific process of verifying the metric property includes steps as follows:
1. Pre-pressurizing: pre-add the load to 100 t at a time or using a loading vehicle not less than 50 t to go back and forth to a loading implement not less than three times;
2. The accuracy of the zero setting and the tare excluding device;
3. The zero setting before loading;
4. The weighing property:
4.1 A repeatability test of the weighing machine during the verification by adopting the standard counterweight and the substitution to confirm the amount of the standard counterweight: First, check the repeatability of the weighing point at 50 t and add a 50 t standard counterweight on the loading implement for three times. If the error of the repeatability is not larger than 0.3 e, the standard counterweight 3′ is able to be reduced to 35% of the maximal weighing measure. If the repeatability is not larger than 0.2 e, the standard 3′ is able to be reduced to 20% of the maximal weighing measure;
4.2 The weighing test: Add the counterweights or the substitutions 3′ from zero to 100 t in order from small to big and remove the counterweights to zero by the same way. The test should choose five verification points at 1 t, 25 t, 50 t, 75 t, and 100 t;
4.3 The tare-excluding weighing test: At least 2 different tare weights are examined by the tare-excluding weighing test. According to step 4.2, the test points are 1 t, 50 t, the weight of maximal permissible error, the possible maximal net weight, and 80 t;
4.4 The eccentricity test: Put the standard counterweight 3′ with a weight of 14 t on the eight eccentric test areas 251′-258′ by turns for testing until the errors of the indicated values of the eight eccentric test areas 251′-258′ are all not larger than 50 kg;
4.5 The discrimination test: Proceed the test at the weighing points 1 t, 50 t, and 100 t and the verification at the same time; and
4.6 The repeatability test: Proceed to test in two respective groups of the weight at 50 t and the weight closed to the maximal weight (90 t). Each group should be repeatedly tested at least three times.
From the verifications mentioned above, a tonnage of the standard counterweights or the substitutions that need to be transported such as (1)A weight of 100 t is transported in the pre-pressurizing step; (2)A weight of 150 t is transported in the step 4.1 for the repeatability test of the weighing machine during the verification by adopting the standard counterweight and the substitution to confirm the amount of the standard counterweight; (3)A weight of 100 t is transported in the step 4.2 for the weighing test; (4)A weight of 160 t is transported in the step 4.3 for the tare-excluding weighing test; (5)A weight of 112 t is transported in the step 4.4 for eccentricity test; (6)A weight of 270 t is transported in the step 4.6 for the repeatability test.
Therefore, the disadvantages existed in the conventional method of adopting the standard counterweights or the substitutions of the counterweight to verify a fixed electronic weighing machine are described as follows:
1. Heavy workload and the extremely low efficiency. To verify a qualified 100 t fixed electronic truck scale requires counterweights and substitutions in a weight of 932 t. If it is not qualified, the truck scale should be adjusted and then be re-verified, namely moving the counterweights again. The weight of moving the counterweights requires over thousands tons.
2. Poor safety of moving a large number of counterweights or the substitutions. Due to the limited loading surface of the electronic truck scale, such as 54 square gauges of the loading surface for a 100-ton electronic truck scale, it is hard to put 100 tons of counterweights or substitutions on a limit area and is dangerous during loading and unloading the counterweights or the substitutions;
3.Difficulty of finding substitutions. Not every user of large-scale electronic truck scales can find suitable substitutions. For example, stand scale installed at the side of the highway is hard to find a suitable substitution, users for railway, harbor, toxic liquid, gaseous chemical industry, textile factory, and coal mine etc. are also hard to find the suitable substitutions;
4. Difficulty of transporting the standard counterweight. To verify a 100-ton truck scale requires transporting counterweight for at least 50 tons. To verify a 150-ton truck scale requires transporting counterweight for at least 75 tons. In current practice, it can only transport the counterweight at about 15 tons once. The amount of the transportation for once is especially limited in the mountain area with bridge load-limit, road load-limit, topography load-limit, and installation in the ravine (such as mine) etc.
5.Extremely high costs. To transport and move such a large number of standard counterweights and substitutions requires many verification scale vehicles and cranes and spends a few days working with many people to complete the verification. For example, to verify a 100-ton truck scale normally requires 7 workdays.
To sum up, most of the verification organizations in the counties, the cities, and the provinces do not have enough standard counterweights for the large-scale weighing machine (such as the 150-ton electronic truck scale). Even though there are enough standard counterweights, the safety for loading and unloading the counterweights and transporting the counterweights and the transportation costs cannot be ensured under the current technique. Secondly, even if the counterweights are transported to the destination, to proceed the verification according to the verification regulations of the digit indicator weighing machine stipulated by JJG539-1997 requires a heavy verification workload and takes a long time to verify, which is unable to be ensured to follow the verification regulation. Therefore, the conventional method for verifying a large-scale fixed electronic weighing machine by adopting the standard counterweights and the substitutions of the standard counterweights can be improved.